I would like to share my implementation of a smokey Perlin Noise effect inDefold
99% of the work is done in a fragment shader - there is one script that updates the time uniform every update. You will find the link to the fragment shader in the readme.
I believe my code is verbose and non-optimal, but as an example implementation I think it works quite well and the effect it generates is rather pleasing 
If you want to learn how I did this, I found this video very helpful when developing this solution: https://www.youtube.com/watch?v=MJ3bvCkHJtE&